1. Field of the Invention
The invention relates to a flow-forming method, in which a preform or blank is fixed to a spinning chuck and is formed or worked by means of at least one rolling member, the blank rotating about a rotation axis relative to the rolling member. The invention also relates to a flow-forming device having a forming device with at least one rolling member, a spinning chuck on which is held a blank and which is axially displaceable relative to the forming device and a drive for rotating the blank relative to the forming device.
2. Discussion of the Background Art
DE 42 18 092 Cl and DE 196 36 567 A1 describe a method for the manufacture of a circular cylindrical gear part, on a part of whose axial length are formed internal teeth by flow-forming. With this method, a part can be manufactured in a very reasonable manner, which could otherwise only be manufactured at high cost by a cutting procedure. The advantage of manufacture by flow-forming is a virtually final contour-near production, accompanied by a high dimensional stability and a limited peak-to-valley height of the parts produced. Simultaneously material hardening is brought about in the region near to the surface, which has a favorable affect on the wear performance and fatigue strength. During forming, the blank is spun in the tooth profile of a tool by means of one or more spinning rollers, the teeth being completely filled. However, the high loading of the tooth profile of the tool is disadvantageous in this manufacturing procedure. When rolling in the internal teeth, as a result of the penetration of material into the tool tooth profile, bending and impact stress occurs to the teeth. The repeatedly occurring alternating loads lead to tool material fatigue. Ultimately cracks form and the tool fails after a short time. These processes are described in detail in DE 197 13 440 A1.
Tools are also known for planishing and workhardening which are based on hydrostatically mounted spherical tools. With the aid of such tools, a plasticizing of metallic surfaces is brought about by balls or rollers, so that marginal areas can be smoothed or workhardened. As a result of the different embodiments of such tools, it is possible to machine variably designable surfaces (e.g. straight or spherical plane surfaces or bores). The forming of larger material volumes and consequently the shaping of new geometries is not possible with such tools because material plasticizing is impossible due to the manufacturing method used. The transmittable forces are too small for this purpose. Each individual forming or working roll is separately mounted. This construction is unsuitable for the shaping and working of larger material volumes.
Methods are also known in which a blank is flow-formed to its external diameter using one or more rollers, the material penetrating the profile of the tool chuck. Another method proposes the axial fixing of the blank and reducing the diameter thereof accompanied by a radial infeed. As a result of the axial fixing the material flows radially as a result of the pressure of the rollers, so that it is pressed into the recesses of the tool chuck.
In all the aforementioned methods, use is made of individually mounted or seated rollers, which roll with their external-diameter on the blank. As a result of the geometrical and strength-caused dimensions of the rollers with their bearings, as a function of the circumference of the blank, only a limited number of rollers can be arranged in a minimum spacing. Due to the geometrically caused spacing between the rollers, it is impossible to completely compensate the bulging of the circumference of the blank due to the high tangential force in this area and the associated material displacement. Thus, alternating loads occur in the vicinity of tool chuck recesses.
Particularly with working teeth with small modules, this alternating loading can lead to material fatigue and therefore to a short lifespan of the tool.